Rechargeable electric battery packs (also referred to herein simply as battery packs) typically comprise a series of sealed electrochemical energy storage cells. A rechargeable electric battery will degrade or deteriorate over time and with usage due to various factors including for example, the average voltage output energy throughput by the rechargeable electric battery, the temperature of the battery and state of charge.
US2011/0112781 to GM Global Technology discloses a method of gathering information from battery sensors, for instance, information regarding the state-of-charge (SOC); temperature; and/or other characteristics of a vehicle. The information is used to estimate or predict battery degradation or battery state-of-health (SOH). US2012/0078549 to Hyundai Motor Company discloses another method of estimating the state-of-health of a battery of a vehicle based upon measuring the temperature of the battery over time. A degree of deterioration of a battery is estimated from temperature change and travelling distance and the state-of-health of the battery. The remaining travelling distance of a vehicle comprising the battery is then said to be accurately estimated.
A rechargeable electric battery is an important component and the performance of a vehicle comprising such a battery may be determined by the quality of the rechargeable electric battery. Furthermore, a rechargeable electric battery is a high-cost component and the raw material used in the manufacture of the electrochemical storage cells (typically Lithium) can be costly to obtain and may be of limited supply. It is desirable to have rechargeable electric battery systems that are energy efficient. It is also desirable to maximise the length of time a rechargeable electric battery can be used (and/or to maximise the travelling distance that the rechargeable electric battery can provide). Indeed legislation, for example in the USA, is beginning to specify a minimum charging capacity that a rechargeable electric battery used in a vehicle must achieve after a period of use, for example 10 years.
The present invention seeks to provide an improvement in the field of rechargeable electric battery packs by providing a system for optimising the energy efficiency of the rechargeable electric battery and/or to optimising the lifetime of the rechargeable electric battery, that may be used in vehicles.
The invention may be utilised in applications other than for vehicles and passenger vehicles where rechargeable battery packs are used, for example, the rechargeable battery pack of the invention may find advantageous application in: commercial or utility vehicles, such as fork-lift-trucks; electricity grid storage; portable power generators; and back-up power supplies, for example in telecommunications applications.